Liquid crystal displays (LCDs) generally display images by transmitting or blocking light through the action of liquid crystals. LCDs have been used in a variety of computing displays and devices, including notebook computers, desktop computers, tablet computing devices, mobile phones (including smart phones) automobile in-cabin displays, on appliances, as televisions, and so on. LCDs often use an active matrix to drive liquid crystals in a pixel region. In some LCDs, a thin-film transistor (TFT) is used as a switching element in the active matrix.
For fabrication of the AMLCD, the conventional manufacturing process selectively uses a relatively thick color filter, because its dielectric constant is normally about twice of the dielectric constant of a photoactive compound (PAC), which has a relatively low dielectric constant. Generally, the color filter array is about 3 μm to 4 μm thick. Such a large thickness of the color filter array (COA) reduces the coupling between common electrode and data line (CD). This CD coupling depends upon the capacitance between common electrode and the data line, and is proportional to the dielectric constant of the color filter, and is inversely proportional to the thickness of the color filter.
There are several issues with thicker COA for fringe field switching (FFS) mode. First, it is difficult to coat a thick COA. Second, the large thickness of the COA may require alignment of the color filter array with TFTs, which is an additional step in the process. Third, the large thickness of the color filter array also makes difficult to fill via holes such that the via holes need to be larger to enable completely filling the via holes. Fourth, larger via hole sizes may be required as a result of thicker COA. The larger via holes may reduce a ratio of aperture area to via hole area, which reduces the optical transmission or brightness of the AMLCD. Additionally, the deep via holes may cause non-uniformity in a planarization layer that covers the via holes and the color filter array. Liquid crystal molecules are arranged on the top of the planarization layer.
Therefore, it is desirable to develop techniques to reduce the thickness of the COA and to improve optical transmission and performance of the AMLCD.